Self-repairing joints on horizon

When
Kofi Annan
was Secretary-General of the UN, he designated the years from 2000 to 2010 as the Bone and Joint Decade. This was designed to draw attention to the epidemic of bone and joint disease and its projected increase as people live to greater ages.

Now, as the decade closes, American scientists have surprised the world by showing it is possible to harness the body’s own resources to restore a failing joint.

Using rabbits, they have shown how the animal’s own stem cells can be directed to a joint where they regenerate cartilage and bone in separate layers.

The scientists removed the forelimb thigh joint of 10 rabbits and then implanted scaffolds in place of the joints. These three-dimensional scaffolds were made of biological material and were infused with growth factor, a naturally occurring substance that can stimulate cellular growth.

The rabbits’ own stem cells were “homed" by this growth factor. They arrived at the ailing joint and did their work.

Between three and five weeks later, the rabbits were able to move about almost as well as animals that had not undergone the procedure.

It was a radical application of tissue engineering because no pre-prepared stem cells were injected. Rather, the scientists relied on stem cells within the rabbits’ own body to home into the site.

The study is reported in The Lancet where an editorial describes it “as a renaissance of the use of the host as a bioreactor" and says, in theory, it is translatable to humans.

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With osteoarthritis on the rise, increasing numbers of people need new joints. But there is a danger many will outlive their new joints and need another gruelling operation when they are older and have less bone left to support another stainless steel or titanium device.

There are also worries about infection and loosening of the joint in people who are active.

While there has previously been talk of growing individually customised biological joint replacements in the laboratory this study suggests a new path.

The editorial, by Patrick Warnke, of Bond University, who also heads the multinational tissue-engineering network, Myjoint, funded by the European Union, says there are potential problems in extrapolating this latest technique to humans.

The young rabbits had a healthy capacity for natural regeneration. Elderly people, particularly those with diabetes, would not have the same capacity.

Further, the long period of immobility during human joint regeneration would present a risk.

He suggests this risk could possibly be reduced by allowing the patient to continue using the old joint while simultaneously growing a new one elsewhere in the body and transplanting it when appropriate.

This has been done before with a customised mandible used to repair a defect after surgery for a tumour in the floor of the mouth.

While the decade’s bony problems are not solved, Warnke says the rabbit study gives an insight into what might be on the horizon.